DE 10 2008 032 950 B3 describes a self-pumping, hydro-pneumatic suspension strut with internal level regulation, in particular for motor vehicles, which has an oil-filled working cylinder pressurized by the pressure of at least one gas cushion arranged in a high-pressure chamber and acting as a spring, which is divided into two working spaces by a working piston carried by a hollow piston rod, with a piston pump which is driven by spring movement and delivers oil from a low-pressure chamber into the working space connected to the high-pressure chamber, which is provided with a first flow connection that connects the high-pressure chamber to the low-pressure chamber, wherein a further, axially separated second flow connection that can connect the high-pressure chamber to the low-pressure chamber is provided, which can be switched on or off by means of a valve.
By virtue of the two flow connections, the vehicle body of a motor vehicle can be positioned at two different levels, namely a normal level for slow driving and a lower level for driving at high speed. When starting to drive on an uneven road, oil is pumped out of the low-pressure chamber into the high-pressure chamber until a bypass suppresses the work of the pump and thus the level is controlled. The maximum and minimum heights of the vehicle body are determined by the position of the bypass and the outlet openings. If the vehicle is unloaded, the piston rod springs outward, so that the outlet opening that has been freed produces a pressure equalization between the high-pressure and low-pressure chambers. The vehicle body then sinks again to its unladen condition height.
In this known suspension, the strut oil and low-pressure gas cushion are not separated from one another in the low-pressure chamber. Accordingly, this suspension strut can only be used in a mounting position in which the axially movable piston rod projects upward out of the working cylinder. Furthermore, to set different levels, it is necessary to have an external, controllable valve.